Why did menopause evolve? Because selection is more efficient on traits that appear early in life. Mutations that have an effect early in life will increase fitness much more than mutations that manifest late. Most people have already reproduced before any disease manifest; this means that parents will pass their alleles to their offsprings before they show any fitness problems, and it is therefore "too late" for selection. The two theories; non-adaptive, and adaptive, are used to explain the evolution of senescence, which is the decline in reproduction with age. The non-adaptive theory assumes that the evolutionary deterioration of human age occurs as a result of accumulation of deleterious mutations in the germline. These deleterious mutations start expressing themselves late in life, by the time we are weak/wobbly and have already reproduced, this means that Natural selection cannot act on them because reproduction has ended. Studies done on Drosophila melanogaster have shown an inverse relationship between the mean optimal age at maturity and mutation rates per gene. Mutation accumulation affects the allocation of energy, and time that are directed towards growth and reproduction over the lifetime of an organism, especially the period of reproductive lifespan due to the fact that mutation accumulation accelerates senescence, this means that organisms must reach the optimum age of maturity at a younger age as their reproductive lifespan is shortened with accumulated mutation. Mutations happen, and they are completely random with respect to a need in the environment and fitness. Mutations can either be beneficial in which they increase an organism's fitness, neutral in which they do not affect an organism's fitness or deleterious where they negatively affect an organism's fitness. Previously done experiments have shown that most mutation accumulations are deleterious, and just a few are beneficial. Mutations of genes that interact with one another during the developmental process create biological and, thus, phenotypical diversities. Mutations is genetic information that are expressed among organisms via gene expression, which is the translation of genetic information into a phenotypic character. Evolution is the change in a heritable trait in a population across generations since mutations generate variations in the heritable traits; they are considered the raw material for evolution. Therefore, beneficial mutation accumulations during the developmental processes could generate more phenotypic variations, which increases their gene frequency and affect the capacity of phenotypic evolution. Somatic cells The somatic mutation theory of ageing states that accumulation of